FIG. 1 shows a superhard component 100 that is insertable within a downhole tool (not shown) in accordance with an exemplary embodiment of the invention. One example of a superhard component 100 is a cutting element 100, or cutter, for rock bits. The cutting element 100 typically includes a substrate 110 having a contact face 115 and a cutting table 120. The cutting table 120 is fabricated using an ultra hard layer which is bonded to the contact face 115 by a sintering process. The substrate 110 is generally made from tungsten carbide-cobalt, or tungsten carbide, while the cutting table 120 is formed using a polycrystalline ultra hard material layer, such as polycrystalline diamond (“PCD”) or polycrystalline cubic boron nitride (“PCBN”). These cutting elements 100 are fabricated according to processes and materials known to persons having ordinary skill in the art.
Common problems associated with these cutters 100 include chipping, spalling, partial fracturing, cracking, and/or flaking of the cutting table 120. These problems result in the early failure of the cutting table 120. Typically, high magnitude stresses generated on the cutting table 120 at the region where the cutting table 120 makes contact with earthen formations during drilling can cause these problems. These problems increase the cost of drilling due to costs associated with repair, production downtime, and labor costs. For these reasons, testing methods have been developed to ascertain the abrasion resistance and/or impact resistance of cutters 100 so that improved cutter longevity is achieved and the problems discussed above are substantially reduced.
Superhard components 100, which include polycrystalline diamond compact (“PDC”) cutters 100, have been tested for abrasive wear resistance through the use of two conventional testing methods. The PDC cutter 100 includes the cutting table 120 fabricated from polycrystalline diamond. FIG. 2 shows a lathe 200 for testing abrasive wear resistance using a conventional granite log test. Although one exemplary apparatus configuration for the lathe 200 is provided, other apparatus configurations can be used without departing from the scope and spirit of the exemplary embodiment.
Referring to FIG. 2, the lathe 200 includes a chuck 210, a tailstock 220, and a tool post 230 positioned between the chuck 210 and the tailstock 220. A target cylinder 250 has a first end 252, a second end 254, and a sidewall 258 extending from the first end 252 to the second end 254. According to the conventional granite log test, sidewall 258 is an exposed surface 259 which makes contact with the superhard component 100 during the test. The first end is coupled to the chuck 210, while the second end 254 is coupled to the tailstock 220. The chuck 210 is configured to rotate, thereby causing the target cylinder 250 to also rotate along a central axis 256 of the target cylinder 250. The tailstock 220 is configured to hold the second end 254 in place while the target cylinder 250 rotates. The target cylinder 250 is fabricated from a single uniform material, which is typically granite. However, other single uniform rock types have been used for the target cylinder 250, which includes, but is not limited to, Jackforck sandstone, Indiana limestone, Berea sandstone, Carthage marble, Champlain black marble, Berkley granite, Sierra white granite, Texas pink granite, and Georgia gray granite. These target cylinders 250 are costly to acquire, shape, ship, and handle.
The PDC cutter 100 is fitted to the lathe's tool post 230 so that the PDC cutter 100 makes contact with the target cylinder's 250 exposed surface 259 and drawn back and forth across the exposed surface 259. The tool post 230 has an inward feed rate on the target cylinder 250. The abrasive wear resistance for the PDC cutter 100 is determined as a wear ratio, which is defined as the volume of target cylinder 250 that is removed to the volume of the PDC cutter 100 that is removed. Alternatively, instead of measuring volume, the distance that the PDC cutter 100 travels across the target cylinder 250 can be measured and used to quantify the abrasive wear resistance for the PDC cutter 100. Alternatively, other methods known to persons having ordinary skill in the art can be used to determine the wear resistance using the granite log test. Operation and construction of the lathe 200 is known to people having ordinary skill in the art. Descriptions of this type of test is found in the Eaton, B. A., Bower, Jr., A. B., and Martis, J. A. “Manufactured Diamond Cutters Used In Drilling Bits.” Journal of Petroleum Technology, May 1975, 543-551. Society of Petroleum Engineers paper 5074-PA, which was published in the Journal of Petroleum Technology in May 1975, and also found in Maurer, William C., Advanced Drilling Techniques, Chapter 22, The Petroleum Publishing Company, 1980, pp. 541-591, which is incorporated by reference herein. This granite log test was adequate during the initial stages of PDC cutter 100 development. However, PDC cutters 100 have become more resistant to abrasive wear as the technology for PDC cutters 100 improved. Current technology PDC cutters 100 are capable of cutting through many target cylinders 250 without ever developing any appreciable and measurable wear flat; thereby, making the conventional granite log test method inefficient and too costly for measuring the abrasive wear resistance of superhard components 100.
FIG. 3 shows a vertical boring mill 300 for testing abrasive wear resistance using a vertical boring mill (“VBM”) test or vertical turret lathe (“VTL”) test. Although one exemplary apparatus configuration for the VBM 300 is provided, other apparatus configurations can be used without departing from the scope and spirit of the exemplary embodiment. The vertical boring mill 300 includes a rotating table 310 and a tool holder 320 positioned above the rotating table 310. A target cylinder 350 has a first end 352, a second end 354, and a sidewall 358 extending from the first end 352 to the second end 354. According to the conventional VBM test, second end 354 is an exposed surface 359 which makes contact with a superhard component 100 during the test. The target cylinder 350 is typically about thirty inches to about sixty inches in diameter.
The first end 352 is mounted on the lower rotating table 310 of the VBM 300, thereby having the exposed surface 359 face the tool holder 320. The PDC cutter 100 is mounted in the tool holder 320 above the target cylinder's 350 exposed surface 359 and makes contact with the exposed surface 359. The target cylinder 350 is rotated as the tool holder 320 cycles the PDC cutter 100 from the center of the target cylinder's 350 exposed surface 359 out to its edge and back again to the center of the target cylinder's 350 exposed surface 359. The tool holder 320 has a predetermined downward feed rate. The VBM method allows for higher loads to be placed on the PDC cutter 100 and the larger target cylinder 350 provides for a greater rock volume for the PDC cutter 100 to act on. The target cylinder 350 is typically fabricated entirely from granite; however, the target cylinder can be fabricated entirely from another single uniform material that includes, but is not limited to, Jackforck sandstone, Indiana limestone, Berea sandstone, Carthage marble, Champlain black marble, Berkley granite, Sierra white granite, Texas pink granite, and Georgia gray granite. As previously mentioned, these target cylinders 350 are costly to acquire, shape, ship, and handle.
The abrasive wear resistance for the PDC cutter 100 is determined as a wear ratio, which is defined as the volume of target cylinder 350 that is removed to the volume of the PDC cutter 100 that is removed. Alternatively, instead of measuring volume, the distance that the PDC cutter 100 travels across the target cylinder 350 can be measured and used to quantify the abrasive wear resistance for the PDC cutter 100. FIG. 10 shows a graphical wear curve representation 1000 using conventional target cylinders 250 and 350 (FIGS. 2 and 3).
Referring to FIG. 10, the graphical wear curve representation 1000 has a distance travelled x-axis 1010, a weight lost y-axis 1015, and a volume lost y-axis 1020. The distance travelled x-axis 1010 represents the distance that the PDC cutter 100 (FIG. 1) travels across the conventional target cylinder 250 and 350 (FIGS. 2 and 3) and is measured in meters. The weight lost y-axis 1015 represents the weight that the conventional target cylinder 250 and 350 loses as the PDC cutter 100 travels across the conventional target cylinder 250 and 350 and is measured in milligrams. The volume lost y-axis 1020 represents the volume that the conventional target cylinder 250 and 350 loses as the PDC cutter 100 travels across the conventional target cylinder 250 and 350 and is measured in cubic millimeters. The relationship between the distance travelled by the PDC cutter 100 and the weight lost by the conventional target cylinder 250 and 350 is illustrated by a distance and weight curve 1030. The relationship between the distance travelled by the PDC cutter 100 and the volume lost by the conventional target cylinder 250 and 350 is illustrated by a distance and volume curve 1035. Both the distance and weight curve 1030 and the distance and volume curve 1035 are provided based upon the following parameters: 1) 13.4 millimeter PDC cutter diameter; 2) 2 millimeter depth of cut; and 3) a 1.8 meters per second average linear speed. As seen in the graphical wear curve representation 1000, both the distance and weight curve 1030 and the distance and volume curve 1035 have uniform increasing wear because the conventional target cylinder 250 and 350 is fabricated using a uniform material and the effect of any impact of the PDC cutter 100 on the conventional target cylinder 250 and 350 is minimized.
Alternatively, other methods known to persons having ordinary skill in the art can be used to determine the wear resistance using the VBM test. Operation and construction of the VBM 300 is known to people having ordinary skill in the art. A description for this type of testing can be found in Bertagnolli, Ken and Vale, Roger, “Understanding and Controlling Residual Stresses in Thick Polycrystalline Diamond Cutters for Enhanced Durability,” US Synthetic Corporation, 2000, which is incorporated by reference in its entirety herein.
In addition to testing for abrasive wear resistance, PDC cutters 100 can also tested for resistance to impact loading. FIG. 4 shows a drop tower apparatus 400 for testing impact resistance of superhard components using a “drop test” method. The drop test method attempts to emulate the type of loading that can be encountered when the PDC cutter 100 transitions from one formation to another or experiences lateral and axial vibrations.
Referring to FIG. 4, the drop tower apparatus 400 includes a superhard component 100, such as a PDC cutter, a target fixture 420, and a strike plate 450 positioned above the superhard component 100. The PDC cutter 100 is locked into the target fixture 420. The strike plate 450, or weight, is typically fabricated from steel and is positioned above the PDC cutter 100. However, the strike plate 450 can be fabricated from alternative materials known to persons having ordinary skill in the art. The PDC cutter 100 is typically held at a backrake angle 415 with the diamond table 120 of the PDC cutter 100 angled upward towards the strike plate 450. The range for the backrake angle 415 is known to people having ordinary skill in the art.
The strike plate 450 is repeatedly dropped down on the edge of the PDC cutter 100 until the edge of the PDC cutter 100 breaks away or spalls off. These tests are also referred to as “side impact” tests because the strike plate 450 impacts an exposed edge of the diamond table 120. Failures typically appear in either the diamond table 120 or at the contact face 115 between the diamond table 120 and the carbide substrate 110. The “drop test” method is very sensitive to the edge geometry of the diamond table 120. If the table 120 is slightly chamfered, the test results can be altered considerably. The total energy, expressed in Joules, expended to make the initial fracture in the diamond table 120 is recorded. For more highly impact resistant cutters 100, the strike plate 450 can be dropped according to a preset plan from increasing heights to impart greater impact energy on the cutter 100 to achieve failure. However, this “drop test” method embodies drawbacks in that this method requires that many cutters 100 be tested to achieve a valid statistical sampling that can compare the relative impact resistance of one cutter type to another cutter type. The test is inadequate in providing results that reflect the true impact resistance of the entire cutter 100 as it would see impact loads in a downhole environment. The test exhibits a static impact effect whereas the true impact is dynamic. The number of impacts per second can be as high as 100 hertz (“Hz”).
In view of the foregoing, there is a need in the art for providing an improved testing method for abrasive wear resistance of a superhard component. There also is a need in the art for providing an improved testing method for impact resistance of a superhard component. Further, there is a need in the art for providing testing methods for abrasive wear resistance and/or impact resistance of a superhard component that is repeatable, efficient, and more economical.
The drawings illustrate only exemplary embodiments of the invention and are therefore not to be considered limiting of its scope, as the invention may admit to other equally effective embodiments.